ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

root/jsr166/jsr166/src/jsr166y/ForkJoinTask.java

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.31 by jsr166, Sun Aug 2 22:58:50 2009 UTC vs.
Revision 1.34 by dl, Tue Aug 4 11:44:33 2009 UTC

#	Line 12 | Line 12 | import java.io.Serializable;
12		import java.util.Collection;
13		import java.util.Collections;
14		import java.util.List;
15	+	import java.util.RandomAccess;
16		import java.util.Map;
17		import java.util.WeakHashMap;
18
#	Line 54 | Line 55 | import java.util.WeakHashMap;
55		* restriction is in part enforced by not permitting checked
56		* exceptions such as {@code IOExceptions} to be thrown. However,
57		* computations may still encounter unchecked exceptions, that are
58	<	* rethrown to callers attempting join them. These exceptions may
58	>	* rethrown to callers attempting to join them. These exceptions may
59		* additionally include RejectedExecutionExceptions stemming from
60		* internal resource exhaustion such as failure to allocate internal
61		* task queues.
#	Line 85 | Line 86 | import java.util.WeakHashMap;
86		* established in a constructor, and then defines a {@code compute}
87		* method that somehow uses the control methods supplied by this base
88		* class. While these methods have {@code public} access (to allow
89	<	* instances of different task subclasses to call each others
89	>	* instances of different task subclasses to call each other's
90		* methods), some of them may only be called from within other
91		* ForkJoinTasks (as may be determined using method {@link
92		* #inForkJoinPool}).  Attempts to invoke them in other contexts
93		* result in exceptions or errors, possibly including
94		* ClassCastException.
95		*
96	<	* <p>Most base support methods are {@code final} because their
97	<	* implementations are intrinsically tied to the underlying
98	<	* lightweight task scheduling framework, and so cannot be overridden.
99	<	* Developers creating new basic styles of fork/join processing should
100	<	* minimally implement {@code protected} methods
101	<	* {@link #exec}, {@link #setRawResult}, and
102	<	* {@link #getRawResult}, while also introducing an abstract
103	<	* computational method that can be implemented in its subclasses,
104	<	* possibly relying on other {@code protected} methods provided
104	<	* by this class.
96	>	* <p>Most base support methods are {@code final}, to prevent
97	>	* overriding of implementations that are intrinsically tied to the
98	>	* underlying lightweight task scheduling framework.  Developers
99	>	* creating new basic styles of fork/join processing should minimally
100	>	* implement {@code protected} methods {@link #exec}, {@link
101	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
102	>	* an abstract computational method that can be implemented in its
103	>	* subclasses, possibly relying on other {@code protected} methods
104	>	* provided by this class.
105		*
106		* <p>ForkJoinTasks should perform relatively small amounts of
107	<	* computations, otherwise splitting into smaller tasks. As a very
108	<	* rough rule of thumb, a task should perform more than 100 and less
109	<	* than 10000 basic computational steps. If tasks are too big, then
110	<	* parallelism cannot improve throughput. If too small, then memory
111	<	* and internal task maintenance overhead may overwhelm processing.
107	>	* computation. Large tasks should be split into smaller subtasks,
108	>	* usually via recursive decomposition. As a very rough rule of thumb,
109	>	* a task should perform more than 100 and less than 10000 basic
110	>	* computational steps. If tasks are too big, then parallelism cannot
111	>	* improve throughput. If too small, then memory and internal task
112	>	* maintenance overhead may overwhelm processing.
113		*
114		* <p>This class provides {@code adapt} methods for {@link
115		* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
116		* may be of use when mixing execution of ForkJoinTasks with other
117		* kinds of tasks. When all tasks are of this form, consider using a
118	<	* pool in {@link ForkJoinPool#setAsyncMode}.
118	>	* pool in {@link ForkJoinPool#setAsyncMode async mode}.
119		*
120	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
121	<	* to be used in extensions such as remote execution frameworks. It is
122	<	* in general sensible to serialize tasks only before or after, but
123	<	* not during execution. Serialization is not relied on during
123	<	* execution itself.
120	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
121	>	* used in extensions such as remote execution frameworks. It is
122	>	* sensible to serialize tasks only before or after, but not during,
123	>	* execution. Serialization is not relied on during execution itself.
124		*
125		* @since 1.7
126		* @author Doug Lea
#	Line 382 | Line 382 | public abstract class ForkJoinTask<V> im
382		*/
383		private V reportFutureResult()
384		throws ExecutionException, InterruptedException {
385	+	if (Thread.interrupted())
386	+	throw new InterruptedException();
387		int s = status & COMPLETION_MASK;
388		if (s < NORMAL) {
389		Throwable ex;
#	Line 389 | Line 391 | public abstract class ForkJoinTask<V> im
391		throw new CancellationException();
392		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
393		throw new ExecutionException(ex);
392	–	if (Thread.interrupted())
393	–	throw new InterruptedException();
394		}
395		return getRawResult();
396		}
#	Line 401 | Line 401 | public abstract class ForkJoinTask<V> im
401		*/
402		private V reportTimedFutureResult()
403		throws InterruptedException, ExecutionException, TimeoutException {
404	+	if (Thread.interrupted())
405	+	throw new InterruptedException();
406		Throwable ex;
407		int s = status & COMPLETION_MASK;
408		if (s == NORMAL)
#	Line 409 | Line 411 | public abstract class ForkJoinTask<V> im
411		throw new CancellationException();
412		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
413		throw new ExecutionException(ex);
412	–	if (Thread.interrupted())
413	–	throw new InterruptedException();
414		throw new TimeoutException();
415		}
416
#	Line 529 | Line 529 | public abstract class ForkJoinTask<V> im
529
530		/**
531		* Commences performing this task, awaits its completion if
532	<	* necessary, and return its result.
532	>	* necessary, and return its result, or throws an (unchecked)
533	>	* exception if the underlying computation did so.
534		*
534	–	* @throws Throwable (a RuntimeException, Error, or unchecked
535	–	* exception) if the underlying computation did so
535		* @return the computed result
536		*/
537		public final V invoke() {
#	Line 543 | Line 542 | public abstract class ForkJoinTask<V> im
542		}
543
544		/**
545	<	* Forks the given tasks, returning when {@code isDone} holds
546	<	* for each task or an exception is encountered.
545	>	* Forks the given tasks, returning when {@code isDone} holds for
546	>	* each task or an (unchecked) exception is encountered, in which
547	>	* case the exception is rethrown.  If more than one task
548	>	* encounters an exception, then this method throws any one of
549	>	* these exceptions.  The individual status of each task may be
550	>	* checked using {@link #getException()} and related methods.
551		*
552		* <p>This method may be invoked only from within {@code
553		* ForkJoinTask} computations (as may be determined using method
#	Line 555 | Line 558 | public abstract class ForkJoinTask<V> im
558		* @param t1 the first task
559		* @param t2 the second task
560		* @throws NullPointerException if any task is null
558	–	* @throws RuntimeException or Error if a task did so
561		*/
562		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
563		t2.fork();
#	Line 565 | Line 567 | public abstract class ForkJoinTask<V> im
567
568		/**
569		* Forks the given tasks, returning when {@code isDone} holds for
570	<	* each task or an exception is encountered. If any task
571	<	* encounters an exception, others may be, but are not guaranteed
572	<	* to be, cancelled.
570	>	* each task or an (unchecked) exception is encountered, in which
571	>	* case the exception is rethrown. If any task encounters an
572	>	* exception, others may be, but are not guaranteed to be,
573	>	* cancelled.  If more than one task encounters an exception, then
574	>	* this method throws any one of these exceptions.  The individual
575	>	* status of each task may be checked using {@link #getException()}
576	>	* and related methods.
577		*
578		* <p>This method may be invoked only from within {@code
579		* ForkJoinTask} computations (as may be determined using method
#	Line 575 | Line 581 | public abstract class ForkJoinTask<V> im
581		* result in exceptions or errors, possibly including {@code
582		* ClassCastException}.
583		*
578	–	* <p>Overloadings of this method exist for the special cases
579	–	* of one to four arguments.
580	–	*
584		* @param tasks the tasks
585	<	* @throws NullPointerException if tasks or any element are null
583	<	* @throws RuntimeException or Error if any task did so
585	>	* @throws NullPointerException if any task is null
586		*/
587		public static void invokeAll(ForkJoinTask<?>... tasks) {
588		Throwable ex = null;
#	Line 616 | Line 618 | public abstract class ForkJoinTask<V> im
618		}
619
620		/**
621	<	* Forks all tasks in the collection, returning when {@code
622	<	* isDone} holds for each task or an exception is encountered.
623	<	* If any task encounters an exception, others may be, but are
624	<	* not guaranteed to be, cancelled.
621	>	* Forks all tasks in the specified collection, returning when
622	>	* {@code isDone} holds for each task or an (unchecked) exception
623	>	* is encountered.  If any task encounters an exception, others
624	>	* may be, but are not guaranteed to be, cancelled.  If more than
625	>	* one task encounters an exception, then this method throws any
626	>	* one of these exceptions.  The individual status of each task
627	>	* may be checked using {@link #getException()} and related
628	>	* methods.  The behavior of this operation is undefined if the
629	>	* specified collection is modified while the operation is in
630	>	* progress.
631		*
632		* <p>This method may be invoked only from within {@code
633		* ForkJoinTask} computations (as may be determined using method
#	Line 630 | Line 638 | public abstract class ForkJoinTask<V> im
638		* @param tasks the collection of tasks
639		* @return the tasks argument, to simplify usage
640		* @throws NullPointerException if tasks or any element are null
633	–	* @throws RuntimeException or Error if any task did so
641		*/
642		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
643	<	if (!(tasks instanceof List<?>)) {
643	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
644		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
645		return tasks;
646		}
#	Line 674 | Line 681 | public abstract class ForkJoinTask<V> im
681		}
682
683		/**
684	<	* Returns {@code true} if the computation performed by this task
685	<	* has completed (or has been cancelled).
686	<	*
687	<	* @return {@code true} if this computation has completed
688	<	*/
689	<	public final boolean isDone() {
690	<	return status < 0;
684	<	}
685	<
686	<	/**
687	<	* Returns {@code true} if this task was cancelled.
688	<	*
689	<	* @return {@code true} if this task was cancelled
690	<	*/
691	<	public final boolean isCancelled() {
692	<	return (status & COMPLETION_MASK) == CANCELLED;
693	<	}
694	<
695	<	/**
696	<	* Asserts that the results of this task's computation will not be
697	<	* used. If a cancellation occurs before attempting to execute this
698	<	* task, execution will be suppressed, {@link #isCancelled}
699	<	* will report true, and {@link #join} will result in a
700	<	* {@code CancellationException} being thrown. Otherwise, when
701	<	* cancellation races with completion, there are no guarantees
702	<	* about whether {@code isCancelled} will report {@code true},
703	<	* whether {@code join} will return normally or via an exception,
704	<	* or whether these behaviors will remain consistent upon repeated
705	<	* invocation.
684	>	* Attempts to cancel execution of this task. This attempt will
685	>	* fail if the task has already completed, has already been
686	>	* cancelled, or could not be cancelled for some other reason. If
687	>	* successful, and this task has not started when cancel is
688	>	* called, execution of this task is suppressed, {@link
689	>	* #isCancelled} will report true, and {@link #join} will result
690	>	* in a {@code CancellationException} being thrown.
691		*
692		* <p>This method may be overridden in subclasses, but if so, must
693		* still ensure that these minimal properties hold. In particular,
#	Line 714 | Line 699 | public abstract class ForkJoinTask<V> im
699		* invoke {@link #completeExceptionally}.
700		*
701		* @param mayInterruptIfRunning this value is ignored in the
702	<	* default implementation because tasks are not in general
702	>	* default implementation because tasks are not
703		* cancelled via interruption
704		*
705		* @return {@code true} if this task is now cancelled
#	Line 725 | Line 710 | public abstract class ForkJoinTask<V> im
710		}
711
712		/**
713	+	* Returns {@code true} if the computation performed by this task
714	+	* has completed (or has been cancelled).
715	+	*
716	+	* @return {@code true} if this computation has completed
717	+	*/
718	+	public final boolean isDone() {
719	+	return status < 0;
720	+	}
721	+
722	+	/**
723	+	* Returns {@code true} if this task was cancelled.
724	+	*
725	+	* @return {@code true} if this task was cancelled
726	+	*/
727	+	public final boolean isCancelled() {
728	+	return (status & COMPLETION_MASK) == CANCELLED;
729	+	}
730	+
731	+	/**
732		* Returns {@code true} if this task threw an exception or was cancelled.
733		*
734		* @return {@code true} if this task threw an exception or was cancelled
#	Line 734 | Line 738 | public abstract class ForkJoinTask<V> im
738		}
739
740		/**
741	+	* Returns {@code true} if this task completed without throwing an
742	+	* exception and was not cancelled.
743	+	*
744	+	* @return {@code true} if this task completed without throwing an
745	+	* exception and was not cancelled
746	+	*/
747	+	public final boolean isCompletedNormally() {
748	+	return (status & COMPLETION_MASK) == NORMAL;
749	+	}
750	+
751	+	/**
752	+	* Returns {@code true} if this task threw an exception.
753	+	*
754	+	* @return {@code true} if this task threw an exception
755	+	*/
756	+	public final boolean isCompletedExceptionally() {
757	+	return (status & COMPLETION_MASK) == EXCEPTIONAL;
758	+	}
759	+
760	+	/**
761		* Returns the exception thrown by the base computation, or a
762		* {@code CancellationException} if cancelled, or {@code null} if
763		* none or if the method has not yet completed.
#	Line 832 | Line 856 | public abstract class ForkJoinTask<V> im
856		}
857
858		/**
859	<	* Possibly executes other tasks until this task is ready.
859	>	* Possibly executes other tasks until this task is ready.  This
860	>	* method may be useful when processing collections of tasks when
861	>	* some have been cancelled or otherwise known to have aborted.
862		*
863		* <p>This method may be invoked only from within {@code
864		* ForkJoinTask} computations (as may be determined using method
#	Line 877 | Line 903 | public abstract class ForkJoinTask<V> im
903
904		/**
905		* Possibly executes tasks until the pool hosting the current task
906	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
907	<	* designs in which many tasks are forked, but none are explicitly
908	<	* joined, instead executing them until all are processed.
906	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
907	>	* be of use in designs in which many tasks are forked, but none
908	>	* are explicitly joined, instead executing them until all are
909	>	* processed.
910		*
911		* <p>This method may be invoked only from within {@code
912		* ForkJoinTask} computations (as may be determined using method
#	Line 1023 | Line 1050 | public abstract class ForkJoinTask<V> im
1050		* called otherwise. The return value controls whether this task
1051		* is considered to be done normally. It may return false in
1052		* asynchronous actions that require explicit invocations of
1053	<	* {@link #complete} to become joinable. It may throw exceptions
1054	<	* to indicate abnormal exit.
1053	>	* {@link #complete} to become joinable. It may also throw an
1054	>	* (unchecked) exception to indicate abnormal exit.
1055		*
1056		* @return {@code true} if completed normally
1030	–	* @throws Error or RuntimeException if encountered during computation
1057		*/
1058		protected abstract boolean exec();
1059

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines